Preselect, powershift transmissions of the type having a plurality of multiple ratio power paths alternately connected between input and output shafts are well-known. Such transmissions are well-suited for road vehicles since they may be made relatively compact and inexpensive and since they may be readily powershifted by both manual and automatic controls. Many of these transmissions include two countershafts each defining a power path, two or more ratio gears rotatably mounted on each countershaft with at least one of the gears on one countershaft being a reverse gear and with all of the gears in constant driving relation with the output shaft, a synchronizer clutch associated with each gear and engagable to clutch one gear at a time to each respective countershaft, and two powershift clutches alternately engaged to complete driving connections between the input and output shafts.
Controls for such transmissions (particularly automatic controls) readily provide for automatic, power upshifting and downshifting in the forward speed ratios by establishing a driving connection through one path, engaging or preselecting the next upshift or downshift ratio gear in the other or nondriving path, then switching the driving connection from the one path to the other path by substantially simultaneously engaging and disengaging the powershift clutches respectively associated with the other path and the one path.
However, controls of such transmissions have not readily provided for powershifting between forward and reverse Powershifting between forward and reverse has many advantages, particularly when the transmission is installed in a vehicle which may be occasionally stuck in snow or mud.